Fuel level indicators may be coupled to a fuel tank of an engine system to signal the level of fuel contained in the fuel tank. As such, since various engine controls are based on the amount of fuel available in the engine, an accurate fuel level estimate may be required to enable engine performance to be optimized. Accordingly, diagnostic tests may be periodically performed on the fuel level indicator. If the fuel level indicator output is noisy, the output may not be relied on and a diagnostic code may be set to indicate potential sensor degradation.
However the inventors have recognized that fuel level indicator noise may occur due to various reasons. For example, the noise may be electrical noise arising from a degraded electrical component (e.g., faulty wiring or degraded sensor). As another example, the noise may be mechanical noise arising from sloshing of fuel in the fuel tank due to driving conditions and/or road conditions. Since a diagnostic code is set irrespective of whether the noise is electrical or mechanical, there may be conditions where the noise is transient due to fuel slosh but degradation (and replacement) of the fuel level indicator is nonetheless recommended. As such, this may lead to expensive false warranty issues and customer dissatisfaction.
The inventors herein have recognized that a fuel tank pressure sensor response is magnified during fuel sloshing in a sealed fuel system due to the generation of additional fuel vapors. Therefore, based on correlations between a fuel tank pressure response and a fuel level indicator response in a sealed fuel system, electrical noise may be better differentiated from mechanical noise. In one example, fuel level indicator noise may be addressed by a method for an engine fuel system comprising indicating degradation of a fuel tank fuel level indicator based on each of a fuel level indicator output and a fuel tank pressure sensed in a sealed fuel tank system.
For example, in response to any indication of fuel level indicator noise, an active test may be performed to identify the origin (electrical or mechanical) of the noise. Therein, the fuel system may be sealed, such as by closing a canister vent valve. A fuel tank pressure response in the sealed fuel system may then be compared to the fuel level indicator response. If the fuel level indicator noise correlates with fuel tank pressure fluctuations (e.g., both the fuel level indicator and the pressure sensor are noisy), the indicator noise may be attributed to mechanical noise from fuel slosh. In this case, no diagnostic code is set since the fuel level sensor is not degraded. In comparison, if the fuel level indicator noise does not correlate with fuel tank pressure fluctuations (e.g., the fuel level indicator is noisy but the pressure sensor is not), the noise may be attributed to electrical noise. In this case, a diagnostic code is set since the fuel level sensor may need replacement.
In this way, fuel level indicator noise may be more accurately and reliably identified based on correlations between fuel level indicator noise and fuel tank pressure noise in a sealed fuel system. By relying on the magnification of a fuel tank pressure response during fuel slosh, fuel level indicator mechanical noise may be better distinguished from electrical noise. By appropriately setting a diagnostic code only responsive to electrical noise and not responsive to mechanical noise, false warranty issues may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.